The present invention relates to a motor-driven brake system which is advantageously used for a vehicle.
As a motor-driven brake system, there can be mentioned, for example, a brake system of the type disclosed in Unexamined Japanese Patent Application Public Disclosure No. 3-45462. The brake system of this type comprises a pair of pads disposed at opposite sides of a disk, and a caliper for pressing the pads against the disk to generate a braking force. As the caliper, generally, a so-called floating type caliper which is movable along the axis of the disk is employed.
The floating type caliper comprises: a motor; a first movable member disposed at the opposite side of one pad from the disk and adapted to be moved directly by the motor; and a second movable member supporting the motor and having a claw portion disposed at the opposite side of the other pad from the disk. When the first movable member is moved by the motor to press the one pad against the disk, a reaction force acts to move the second movable member relative to the disk to thereby press the claw portion against the other pad, which is in turn pressed against the disk. Thus, the two pads move from opposite directions and press against the disk, thereby generating a braking force.
However, the above-mentioned floating type caliper poses the following problems:
In order to release the braking force, the motor is operated in a reverse direction, so that the first movable member is moved in a direction for releasing the pressure by which the one pad has applied to the disk. That is, since the first movable member is moved directly by the motor, the one pad which has been pressed by the first movable member is easily moved away from the disk. On the other hand, however, the second movable member which is not moved directly by the motor cannot enable the other pad to be moved away from the disk, so that the other pad drags against the disk. Consequently, not only does the lifetime of the pad and the disk become short, but also fuel consumption becomes high.